Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$249.92	10.683%	$276.619	$276.62	$276.60	$276.60
Purchase #2	$152.91	9.161%	$166.9181	$166.92	$166.90	$166.90
Purchase #3	$162.52	12.813%	$183.3437	$183.34	$183.35	$183.30
Purchase #4	$55.43	4.871%	$58.13	$58.13	$58.15	$58.10
Purchase #5	$82.81	8.154%	$89.5623	$89.56	$89.55	$89.60
Purchase #6	$33.74	6.397%	$35.8983	$35.90	$35.90	$35.90
Purchase #7	$166.50	11.486%	$185.6242	$185.62	$185.60	$185.60
7 purchase totals =	$903.83		$996.0956	$996.09	$996.05	$996.00